Atrazine and its primary metabolites in Swiss lakes: Input characteristics and long-term behavior in the water column

In order to assess the impact of herbicides on aquatic ecosystems, detailed information on the factors that govern the input and the behavior of such chemicals in rivers, lakes, and coastal seawater is required. In this context, we studied the input characteristics (seasonal variation) as well as the distribution and residence time of the herbicides atrazine, simazine, and terbutylazine and of the primary atrazine metabolites hydroxyatrazine, desethylatrazine, and deisopropylatrazine in three Swiss lakes exhibiting quite different catchment areas and/or hydraulic properties. The results obtained from numerous field measurements (period of 5 years, 1990-1994) combined with computer simulations indicate that all compounds investigated showed a conservative behavior in the water column of the lakes (i.e., no elimination other than by flushing), except for a short period in the summer, where some minor elimination occurred in the epilimnion. The major input of both the parent triazine herbicides and the metabolites occurred in the epilimnion during or right after the application period. For atrazine, the most abundant of the three herbicides investigated, it is shown that the total annual input depended strongly on the rainfall during the application period. For a given lake, the annual input varied between 0.5% (dry weather) and 2% (very wet weather) of the total amount applied in the catchment area. For different lakes receiving similar amounts of rainfall, very similar input fractions were found despite the significantly different catchment areas. Among the metabolites, desethylatrazine occurred at levels similar to those for atrazine, while hydroxyatrazine and deisopropylatrazine were present at 2-4 times lower levels. Note that this study provides the first quantitative data on the transport of hydroxyatrazine from soils to surface waters. The results of this study form an important base for assessing or predicting past, present, and future inputs of triazines to lakes for which only limited data are available. Finally, this study demonstrates that small lakes exhibiting a well-characterized catchment area represent excellent experimental field systems for evaluating quantitatively the transport characteristics of herbicides and their metabolites from soils to surface waters and for assessing the persistence of such compounds in surface waters.